This invention relates generally to light emitting devices and methods for making the same. More particularly, this invention relates to light emitting diodes and methods for making the same.
Light emitting devices, such as light emitting diodes (LEDs), are semiconductor devices that generate light from electrical excitation where electrons and holes combine to annihilate, and thereby forming photons. Typically, III-Nitride based light emitting diodes, such as gallium nitride (GaN) based light emitting diodes have been widely used in many applications due to the ability thereof to output light having wavelengths in the ultra-violet (UV), blue and green regimes.
During formation of the gallium nitride based light emitting diodes, gallium nitride is generally directly deposited on substrates, such as sapphire and silicon by metal organic chemical vapor deposition (MOCVD) or molecular-beam epitaxy (MBE). However, the gallium nitride layer on the substrates may crack upon cooling to room temperature, and gallium may have poor wetting on silicon substrate surfaces to cause failure of the formation of the gallium nitride based light emitting diodes.
There have been attempts to solve the issues during deposition of gallium nitride. In one example, transition metal nitride, such as hafnium nitride (HfN) or zirconium nitride (ZrN) are disposed on the substrates to function as a buffer layer prior to the deposition of gallium nitride on the substrate. In another example, hafnium nitride (HfN) or zirconium nitride (ZrN) is embedded into the gallium nitride based light emitting diodes to function as a current spreading layer and a metallic reflector. However, during formation, an interface between gallium nitride and transition metal nitride may not be controlled readily. In addition, transition metal nitride may react with hydrogen (H2) during MOCVD growth, and direct growth of transition metal nitride on the substrates may also be challenging, which cause difficulties and increasing of the cost of the formation of the light emitting diodes.
Therefore, there is a need for new and improved light emitting devices and methods for making the same to make the light emitting devices to have high performance and to reduce difficulties of the formation thereof.